The present invention relates to a method for killing weeds (e.g., kudzu) involving applying to weeds a herbicidally effective amount of a herbicidal composition comprising glyphosate and at least one acetolactate synthase inhibitor (e.g., trifluxosulfuron, pyrithiobac, flumetsulam).
Kudzu, Pueraria montana (Lour.) Merr. variety lobata (Willd.), is a perennial, deciduous, semi-woody vine with a well developed root system (Forseth, I. N., Jr., and A. F. Innis, Critical Reviews in Plant Sciences, 23: 401-413 (2004)). Originating from China and native to Japan, kudzu was introduced to the United States in 1876 at the Centennial Exposition in Philadelphia. During the Great Depression, kudzu was promoted as a means of erosion control. The so-called “miracle vine” grew and spread too fast because it was imported without its natural predators. In 1972, the Department of Agriculture officially declared kudzu a weed. Under ideal weather conditions, a temperate, moderately wet climate, as typically found in the southeastern United States, kudzu overtakes most everything in its path, in the process harming forests by shielding light from trees and distorting the landscape with its accumulated weight. For Southern farmers, landscapers and citizens, it is a major problem. Now infesting over 7 million acres of the southeastern United States, and spreading at a rate of 120,000 acres per year, this plant represents a serious threat to productivity in its growing region.
Each year, a new network of stems and branches develop from overwintering crowns of kudzu tap roots. Crowns may produce up to 30 vines with multiple branches (Anonymous, 2003, Kudzu (Pueraria lobata), http://www.nwcb.wa.gov/weed_info/-Pueraria—lobata.html). Kudzu stems and leaves continuously overgrow each other, forming dense, multi-layered mats that may be more than a meter thick. Nodes and internodes of vines that come in contact with soil may root and form new crowns. Connections between crowns may disintegrate leaving independent ramets (Forseth and Innis 2004), each capable of developing multiple branches. Kudzu vines may grow up to 18 m/yr (Michael, J. L., Pine regeneration with simultaneous control of kudzu, In: Proceedings, 35th Annual Meeting, Southern Weed Science Society, 1982, Atlanta, Ga., pages 282-288) and quickly cover large areas. These morphological traits make mature stands of kudzu one of the most difficult weeds to control (Nelson, L. R., 2003, Kudzu eradication guidelines, http://www.clemson.edu/extfor/-publications/ec656/).
Kudzu eradication is dependent upon killing all crowns because a few surviving crowns can quickly lead to re-establishment. However, injured crowns may not sprout for two years, thus necessitating eradication efforts over several years (Nelson 2003). Any portion of the root system surviving herbicide treatment may produce new growth (Edwards, M. B., Kudzu-ecological friend or foe, In: Proceedings, 35th Annual Meeting, Southern Weed Science Society, 1982, Atlanta, Ga., pages 232-236).
Herbicide programs have mainly focused on mature, actively growing stands of kudzu. In mature stands, it is difficult to achieve adequate herbicide coverage with all living tissues because of dense layers of foliage. For example, in one study thirteen applications of 2,4,5-trichlorophenoxyacetic acid over a five year period was not successful in killing all crowns (Davis, D. E., and H. H. Funderburk, Weeds, 12: 63-65 (1963)). Some herbicides recommended for control of kudzu are unattractive because they have high soil persistence or are highly leachable thus threatening groundwater safety (Berisford, Y. C., et al., Weed Science, 54: 391-400 (2006); Harrington, T. B., et al., Weed Science, 51: 965-974 (2003)).
Thus there is a need for an effective herbicide to control weeds such as kudzu.